In the prior art, pistons for axial and radial piston machines are known that have each a hollow piston chamber open at the base of the piston and filled with a filler piece that is less dense than the material of the piston. The weight saved in this way, in comparison to a solid piston, makes possible greater rates of revolution and thus greater power for the axial or radial piston machine concerned.
These known pistons are manufactured in a technically complicated and therefore very expensive manner by plastic forming, e.g. drop forging, with subsequent machining of the forged blank to form its outer contour, including the head part in the case of spherical head pistons and slipper pistons, and the hollow piston chamber provided for accommodating the filler piece.
With these known pistons it is important that the filler piece is securely held in place under all operating conditions to avoid damage thereof and thus premature breakdown of the piston. This secure fastening is sought through the use of complicated structural and production, and thus expense-increasing, measures.
A piston of this kind is known, for example, from DE-PS 37 32 648 in which annular grooves are turned into the jacket inner surface facing the hollow piston chamber on both sides of a plane containing the transverse center axis of the hollow piston chamber. The filler piece material that is cast into the hollow piston chamber in a liquid state shrinks in the radial and axial directions on cooling. In the axial direction it shrinks against the walls of the grooves and is tensioned against them. The cooled filler piece is thus held by the shrink-fit connection with the groove walls in the hollow piston chamber but exhibits radial clearance as a result of the shrinkage.